OP, you are assuming everyone will be able to get the same deals. For example, I've never seen a Hydra here where I am for less than $400 CAD. Buying used is great until you only get 30% of it's lifespan. Tanks are tricky, because if you don't live close to an LFS that carries the style you want (ie IM or WB), then you gotta ship. The skimmer you have retails for a lot more than $100 here.
Like most hobbies, money usually makes success easier. It's not that expensive to set up a reef, but all those cut corners can end up causing issues. Used equipment is great for new people, but also will have a much shorter shelf life and no warranty. It balances out.
For some, $2.5k to get a nice little reef going is no big deal, to others, it's an entire year's worth of hobby budget (or more).
I think most people compare it to freshwater tanks which, outside of high end planted tanks, are a small fraction of a reef. My fiancee set up my old 15 cube this weekend with light, plants, substrate, etc all for less than I spent on a few frags.